Parents adjust feeding effort in relation to nestling age in the Eurasian Kestrel (Falco tinnunculus)

Auteurs: Ronny Steen, Geir A. Sonerud, Tore Slagsvold
Bron: JOURNAL OF ORNITHOLOGY, 2012, DOI: 10.1007/s10336-012-0838-y
Abstract: In altricial birds, parents are assumed to optimize the total food delivery to the brood given the time constraints set by self-feeding and food collecting. Older nestlings may require more food than younger ones, and nestlings may need more energy when their growth rate is higher. By video monitoring prey deliveries in ten nests of the Eurasian Kestrel (Falco tinnunculus), we examined whether parents adjusted feeding effort in relation to nestling age. Based on published data on the growth and energy intake of Kestrel nestlings, we predicted parental prey mass delivery to peak at a nestling age of 15–17 days. The prediction was supported. The decrease in provisioning rate during the later nestling stages was best explained by nestling age. However, we cannot be conclusive as to whether this was caused by a decrease in nestling food demand, or by a seasonal decrease in the availability of voles, the dominant prey. The change in provisioning was mostly an effect of a change in the number of prey items delivered. However, prey size also tended to decrease with increasing nestling age. This is opposite to what has been found in most non-raptorial altricial birds, and may have been caused by the ability of Kestrel parents to dismember large prey and thus overcome the gape size-restricted swallowing capacity of small nestlings, together with a need to provide smaller prey to older nestlings when they start to feed unassisted.

Mobs Rule for Great Tit Neighbors

Great tits are more likely to join defensive mobs with birds in nearby nests that are 'familiar neighbours' rather than new arrivals, Oxford University research has found.

Many small birds will defend their nests by joint mobbing, where individuals gang up to harass a potential predator. Scientists studying great tit populations in Wytham Woods, Oxfordshire, wondered whether this sort of defensive behaviour might be behind observations showing that birds successfully raised more chicks when they were alongside familiar neighbours -- those that had occupied the nest box next door for several breeding seasons.

Lees meer: ScienceDaily

Foraging success in a wild species of bird varies depending on which eye is used for anti-predator vigilance

Auteur: Guy Beauchamp
Bron: LATERALITY, DOI: 10.1080/1357650X.2011.648194
Abstract: Brain lateralisation in animals with laterally placed eyes often leads to preferential eye use for ecologically relevant tasks such as monitoring predators and companions. Few studies of preferential eye use have been conducted in the wild and it is not clear if such preferences in the wild are widespread, how individuals can benefit from them, and which ecological factors influence their evolution. In a wild species of bird the extent to which foraging success varied depending on which eye is used during concomitant anti-predator vigilance was examined. When foraging in open mudflats, semipalmated sandpipers (Calidris pusilla) are frequently exposed to predation attempts by falcons (Falco spp) that originate from the tree cover bordering mudflats. Sandpipers spread along the receding tideline and can face the riskier side of their habitat primarily with the left or the right eye as they forage. If foraging is mostly incompatible with vigilance, the rate at which prey items are collected should decrease when birds use their less-preferred eye to scan cover. If foraging and vigilance can be carried out simultaneously, time spent foraging should not be affected but the efficiency with which their burrowing amphipod prey are located may be reduced, thus leading to decreased capture rate. Birds facing the riskier side of the habitat with their right eye captured significantly more prey than those scanning the same side with their left eye. Specialised eye use in sandpipers may allow individuals to perform simultaneous tasks, such as foraging and vigilance, more efficiently.

Hypes on the Mudflats

Waders Imitate Each Other

Current distribution models for social animals are inadequate because they do not take into account that species do not just compete with each other but may also attract one another. This is one of the results Eelke Folmer presents in his PhD thesis. Folmer studied 'self-organization' by various species including foraging waders on the Wadden mudflats. Folmer will defend his PhD thesis 'Self-Organization on Mudflats' at the University of Groningen on 20 April 2012.

An ecologist, watching foraging birds on the mudflats through binoculars, cannot help wondering why, for example, a large group of knots is at one specific spot rather than another; and why the curlews are so far apart? Soil samples, observations, and surveys all provide a wealth of data. But finding ecological patterns and regularities in all these data is quite a task. Computer simulations, spatial statistical models and structural equation models may help in sorting out the information and revealing processes of self-organization.

Lees meer: NIOZ